Electron microscopic studies of mummified tissues in amber fossils. American Museum novitates ; no. 3097

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New York, N.Y. : American Museum of Natural History
"The degree and consistency of fine and ultrastructural preservation of primarily soft tissue remains preserved in amber fossils were examined, using scanning (SEM) and transmission electron microscopy (TEM). 16 insects of various taxa and structure were studied with the SEM, as well as 4 plant specimens, which were from two chemically distinct ambers: 25-30 million year old (myo) amber from the Dominican Republic, and ca. 40 myo amber from the Baltic region. A new technique was used for 'exhuming' a specimen in order to examine the in-situ preservation of whole organs and tissues. Remarkable preservation found in both ambers confirmed earlier reports based on a few specimens. Preservation of all soft tissues in Dominican amber insects appears to be more consistent than in Baltic amber insects, several of which were virtually hollow 'casts.' Membranous structures preserved in the insects include air sacs, uncollapsed tracheae, and various portions of the gut, as well as the brain and bundles of muscle fibers in their original origins and insertions. Very little shrinkage was observed. Specialized pockets, the mycangia, in wood-boring beetles (Platypodidae) still possessed spores and conidiophores of their symbiotic fungus. For plants, columnar cells of leaf mesophyll were found in their original positions and sizes, pollen grains retained the exine sculpturing, and mats of epidermal cells were preserved in anthers. At the ultrastructural level, both flight muscle and brain tissues show substantial degradation of cytoplasmic components due to dehydration. Although sarcomeres are easily identifiable in native muscle samples, the sarcomeric repeats disappear upon hydration, indicating that the repeated structures are probably composed of inorganic salts deposited on thick filaments during dehydration. Membranous structures are generally better preserved than proteinaceous ones. Flight muscle mitochondria are particularly well preserved with tracheoles and T tubules also identifiable. Axon tracts in the central nervous system can be distinguished from cytoplasmic regions, and parallel strips of membranes surrounding cytoplasm are abundant in rehydrated brain samples. Mode of tissue preservation appears to be a rapid and thorough fixation and dehydration, sufficient for preserving DNA in amber more consistently than any other kind of fossil. Pollen was not found viable, but the possibility remains that viable bacterial and fungal spores occur in amber"--P. [1]-2.
31 p. : ill. ; 26 cm.
Includes bibliographical references (p. 29-31).